Supporting a glass substrate during electronic device preparation

ABSTRACT

There is disclosed the preparation of an electronic device comprising a gas discharge panel constructed out of two or more glass substrates, each substrate containing at least one array of electrodes. In one preferred embodiment, there is prepared a display/memory panel comprising a dielectric coating or layer applied over an array of electrodes. The panel preparation comprises firing and curing the electrode (with or without a dielectric coating) onto a glass substrate which is supported by a base plate which maintains its surface flatness and lubricity at the elevated firing and curing temperatures such that the relative flatness and smoothness of the glass substrate (and any dielectric coating fired thereon) are enhanced and the uniformity of the panel spacing is improved. The base plate is typically prepared from a refractory or ceramic-like material.

Unite tates atet Salisbury et al.

Oct. 2, 1973 SUPPORTING A GLASS SUBSTRATE DURING ELECTRONIC DEVICE PREPARATION Inventors: Charles W. Salisbury, Risingsun; Jon

D. Schepman, Sylvania; Neil B. Nofziger, Toledo, all of Ohio Assignee: Owens-Illinois, Inc., Toledo, Ohio Filed: Sept. 15, 1971 Appl. No.: 180,929

Related [1.8. Application Data Continuation-in-part of Ser. No. 856,653, Sept. 10, 1969, abandoned.

52 US. Cl. 5/59, 65/374 51 Int. Cl C03c 27/02 58 Field of Search 65/36, 37, 59, 374

[56] I References Cited UNlTED STATES PATENTS 1,865,691 7/1932 Hill 65/37 l,996,442 4/]935 Stanley 65/37 2,359,501 lO/l944 white 65/374 X Primary Examiner-Robert L. Lindsay, Jr. Attorney-Donald Keith Wedding et al.

[57] ABSTRACT There is disclosed the preparation of an electronic device comprising a gas discharge panel constructed out of two or more glass substrates, each substrate containing at least one array of electrodes. In one preferred embodiment, there is prepared a display/memory panel comprising a dielectric coating or layer applied over an array of electrodes.

The panel preparation comprises firing and curing the electrode (with or without a dielectric coating) onto a glass substrate which is supported by a base plate which maintains its surface flatness and lubricity at the elevated firing and curing temperatures such that the relative flatness and smoothness of the glass substrate (and any dielectric coating fired thereon) are enhanced and the uniformity of the panel spacing is improved. The base plate is typically prepared from a refractory or ceramic-like material.

10 Claims, I Drawing Figure PATENTED 2|975 3. 762. 901

INVENTORS NEIL B, NOFZIGER CHARLES W. SALISBURY JON D SCHEPMAN BY 5. 3 2 1m W ATTORNEYS SUPPORTING A GLASS SUBSTRATE DURING ELECTRONIC DEVICE PREPARATION RELATED APPLICATION This is a continuation-impart of copending U.S. patent application Ser. No. 856,653, filed Sept. 10, 1969 now abandoned.

THE INVENTION This invention relates to the preparation of an electronic device. More particularly, this invention relates to the preparation of multiple gas discharge display/- memory panels which have an electric memory and which are also capable of producing a visual display or representation of data such as numerals, letters, television display, radar displays, binary words, etc.

Multiple gas discharge display and/or memory panels of one particular type with which the present invention is concerned are characterized by an ionizable gaseous medium, usually a mixture of at least two gases at an appropriate gas pressure, in a thin gas chamber or space between a pair of opposed dielectric charge storage members which are backed by conductor (electrode) members, the conductor members backing each dielectric member typically being transversely oriented so as to define a plurality of discrete discharge volumes, each constituting a discharge unit.

In some prior art panels the discharge units are additionally defined by surrounding or confining physical structure such as by cells or apertures in perforated glass plates and the like so as to be physically isolated relative to other units. In either case, with or without the confining physical structure, charges (electrons, ions) produced upon ionization of the gas of a selected discharge unit, when proper alternating operating potentials are applied to selected conductors thereof, are collected upon the surfaces of the dielectric at specifically defined locations and constitute an electrical field opposing the electrical field which created them so as to terminate the discharge for the remainder of the half cycle and aid in the initiation of a discharge on a succeeding opposite half cycle of applied voltage, such charges as are stored constituting an electrical memory. l

Thus, the dielectric layers prevent the passage of substantial conductive current from the conductor members to the gaseous medium and also serve as collecting surfaces for ionized gaseous medium charges (electrons, ions) during the alternate half cycles of the AC. operating potentials, such charges collecting first on one elemental or discrete dielectric surface area and then on an opposing elemental or discrete dielectric surface area on alternate half cycles to constitute an electrical memory.

An example of a panel structure containing nonphysically isolated or open discharge units is disclosed in U.S. Letters Pat. No. 3,499,167 issued to Theodore C. Baker et al.

An example of a panel containing physically isolated units is disclosed in the article by D. L. Bitzer and H. G. Slottow entitled The Plasma Display Panel A Digitally Adressable Display With Inherent Memory, Proceeding of the Fall Joint Computer Conference, IEEE, San Francisco, Calif., November, 1966, pp. 541-547. Also reference is made to U.S. letters Patent No. 3,559,190.

In the operation of the panel, a continuous volume of ionizable gas is confined between a pair of dielectric surfaces backed by conductor arrays forming matrix elements. The cross conductor arrays may be orthogonally related (but any other configuration of conductor arrays may be used) to define a plurality of opposed pairs of charge storage areas on the surfaces of the dielectric bounding or confining the gas. Thus, for a conductor matrix having H rows and C columns the number of elemental discharge volumes will be the product H X C and the number of elemental or discrete areas will be twice the number of elemental discharge volumes.

In addition, the panel may comprise a so-called monolithic structure in which the conductor arrays are created on a single substrate and wherein two or more arrays are separated from each other and from the gas eous medium by at least one insulating member. In such a device the gas discharge takes place not between two opposing members, but between two continguous or adjacent members on the same substrate.

It is also feasible to have a gas discharge device wherein some of the conductive or electrode members are in direct contact with the gaseous medium and the remaining electrode members are appropriately, insulated from such gas.

In addition to the matrix configuration, the conductor arrays may be shaped otherwise. Accordingly, while the preferred conductor arrangement is of the crossed grid type as shown herein, it is likewise apparent that where a maximal variety of two dimensionaldisplay patterns is not necessary, as where specific standardized visual shapes (e.g., numerals, letters, words, etc.) are to be formed and image resolution is not critical, the conductors may be shaped accordingly.

The gas is one which produces visible light or invisible radiation which stimulates a phosphor (if visual dis play is an objective) and a copious supply of charges (ions and electrons) during discharge. In an open cell Baker et al. type panel, the gas pressure and the electric field are sufficient to laterallyconfine charges generated on discharge within elemental or discrete dielectric areas within the perimeter of such areas, especially in a panel containing non-isolated units.

As described in the Baker et al. patent, the space between the dielectric surfaces occupied by the gas is such as to permit photons generated on discharge in a selected discrete or elemental volume of gas to pass freely through the gas space and strike surface areas of dielectric remote from the selected discrete volumes, such remote, photon struck dielectric surface areas thereby emitting electrons so as to condition other and more remote elemental volumes for discharges at a uniform applied potential.

With respect to the memory function of a given discharge panel, the allowable distance or spacing between the dielectric surfaces depends, inter alia, on the frequency of the alternating current supply, the distance typically being greater for lower frequencies.

While the prior art does disclose gaseous discharge devices having externally positioned electrodes for initiating a gaseous discharge, sometimes called electrodeless discharge, such prior art devices utilized frequencies and spacings or discharge volumes and operating pressures such that although discharges are initiated in the gaseous medium, such discharges are ineffective or not utilized for charge generation and storage at higher frequencies; although charge storage may be realized at lower frequencies, such charge storage has not been utilized in a display/memory device in the manner of the Bitzer-Slottow or Baker et al. invention.

The term memory margin" is defined herein as where V, is the half amplitude of the smallest sustaining voltage signal which results in a discharge every half cycle, but at which the cell is not bi-stable and V is the half amplitude of the minimum applied voltage sufficient to sustain discharges once initiated.

It will be understood that the basic electrical phenomenon utilized in a display/memory device is the generation of charges (ions and electrons) alternately storable at pairs of opposed or facing discrete points or areas on a pair of dielectric surfaces backed by conduc tors connected to a source of operating potential. Such stored charges result in an electrical field opposing the field produced by the applied potential that created them and hence operate to terminate ionization in the elemental gas volume between opposed or facing discrete points or areas of dielectric surface. The term sustain a discharge means producing a sequence of momentary discharges, one discharge for each half cycle of applied alternating sustaining voltage, once the elemental gas volume has been fired, to maintain alternate storing of charges at pairs of opposed discrete areas on the dielectric surfaces.

In addition, this invention may be utilized in the preparation of gas discharge display devices comprising opposing electrode arrays without dielectric layers; that is, where the electrodes are in direct contact with an ionizable gaseous medium. Such direct contact devices are well known in the prior art. Reference is made to Cold Cathode Glow Discharge Tubes, a text by G. F. Weston, London, .I. W. Arrowsrriith Ltd., 1968.

In the preparation of a gas discharge panel of the types described hereinbefore, an array of conductive electrode members (with or without a dielectric layer) is appropriately applied to a support member comprising a glass substrate, at least two of such glass substrates being sealed together to form the panel assembly. In such preparation and assembly, the electrode members are first applied to the glass substrate. In a display/memory device, at least one dielectric layer is applied over at least one electrode array.

In the fabrication of a gas discharge device, at least two glass substrates are matched up, electrode array to electrode array (or dielectric layer to dielectric layer), with a space or pocket in between. An ionizable gas mixture is then introduced into the space and the space sealed off.

Typically, the electrodes (and the dielectric) are applied to the ass substrate at relatively high elevated temperatures in excess of the glass annealing temperature of the glass substrate, e.g., about l,000 F to about 2,000" F, usually about l,050 F to about l,300 F.

In a multiple gas discharge device, especially a display/memory device, it is important that the spacing of each gas discharge unit be relatively constant; that is, the distance between opposing arrays of electrodes or opposing dielectric surfaces should be substantially equal and uniform. This is especially true in a so-called open unit type device wherein the units are not physically isolated and where there is uninhibited gas flow between the units.

In a gas discharge display/memory device comprising opposed dielectric surfaces, it is important that the spacing for each cell be within a given tolerance in order to insure that each discharge cell has relatively uniform operating characteristics.

In accordance with the practice of this invention, it has been discovered that the overall spacing uniformity and tolerance of the panel is substantially enhanced and greatly improved by firing the electrodes and/or dielectric layer onto a glass substrate supported by a base plate so as to provide and/or maintain the relative surface flatness and contour of such substrate.

More particularly, in accordance with this invention, the electrodes and/or dielectric coating are fired at a high elevated temperature about the annealing temperature of glass onto a glass or ceramic substrate supported by a relatively flat base plate which maintains the geometric shape of its substrate contact surface, e.g. flatness and lubricity, at the elevated firing temperatures such that the relative flatness and smoothness of the glass substrate and the electrodes and/or dielectric coating fired thereon are enhanced, thereby resulting in improved overall panel spacing uniformity.

It is contemplated that the base plate may be constructed out of any suitable material which maintains its flatness and does not warp at the high elevated electrode and dielectric firing temperatures in excess of the annealing temperature of the glass substrate. Likewise, the selected base plate material must have sufficient lubricity at the firing temperatures such that the glass substrate does not stick or otherwise adhere to the base plate. Furthermore, the lubricity must be such that the glass substrate does not readily slide off the base plate.

In one highly preferred practice hereof, there is used a base plate having a substrate contact surface which is unpolished. It has been surprisingly discovered that an unpolished contact surface reduces the tendency of the substrate to adhere or stick to the base plate.

In the practice of this invention, the surface of the base plate must be dust free; that is, it must maintain a dust-free quality during the firing cycles so as to minimize contamination of the electrodes and/or dielectric.

The base plate is typically prepared from a refractory, ceramic, glass, glass-ceramic, or similar material.

In one particular embodiment hereof, the base plate is prepared from a silicon-containing material such as a ceramic lava silicate, most preferably a fired aluminum silicate, e.g. one having a water absorption of 2 to 3 (A.S.T.M. Test No. C373-56), a softening temperature of about 2,9l9 F. (A.S.T.M. Test No. C24-46), a Mohs scale hardness of about 6, a flexural strength of about 9,000 psi (A.S.T.M. Test No. C369-56), and a linear coefficient of thermal expansion of 3.4 X l0 per C. over a range of 25 to 600 C., as disclosed in Technical Bulletin No. 656 of the American Lava Corporation (a subsidiary of 3M Company), Chattanooga, Tenn., 37405 U.S.A. Also reference is made to Chart No. 711, superseding No. 691, published by the American Lava Corporation.

Another ceramic lava silicate used in this invention is fired magnesium silicate (talc), e.g. such as one having a water absorption of 2 to 3, a softening temperature of about 2,687 F., a hardness of about 6, a flexural strength of about 9,000 psi, and a linear coefficient of thermal expansion of l 1.9 X 10" per C. over a range of 25 to 600 C, also disclosed in Technical Bulletin No. 656 and Chart No. 711 of the American Lava Corporation.

In addition there may be used an aluminummagnesium silicate, e.g. such as one disclosed in Tech nical Bulletin No. 651 of the American Lava Corporation.

A wide variety of other silicate materials are also contemplated.

In another particular embodiment hereof, the base plate is prepared from a high pure fused silica having high thermal-shock resistance and low thermal expansion, e.g. such as Slipcast and Densecast SILFRAX fused silica refractories, consisting essentially of about 99 per cent by weight fused silica, as marketed by the .Carborundum Company, Niagara Falls, NY. 14302, U.S.A., Technical Publication Form No. A-2063.

In another particular embodiment hereof, the base plate is prepared from a relatively low thermal expan sion composition consisting essentially of about 75 per cent to about 99 per cent by weight aluminum oxide and about per cent to about 1 per cent by weight silicon oxide, such as the alumina-based materials marketed by Coors'Porcelain Company, Golden, Colo., 80401, U.S.A. and the Norton Company of Worcester, Mass, 01606.

In one specific aluminum oxide-silicon oxide embodiment of the foregoing, there is used a fused composition consisting essentially of about 94 per cent by weight aluminum oxide and about 4 per cent by weight silicon oxide.

In one preferred specific aluminum oxide-silicon oxide embodiment, excellent results have been obtained using a fused composition consisting essentially of about 84 per cent by weight aluminum oxide and about 16 per cent by weight silicon oxide.

In another specific aluminum oxide-silicon oxide embodiment, there is used a fused composition consisting essentially of about 91 .3 per cent by weight aluminum oxide, about 8.5 per cent by weight silicon oxide, about 0.08 per cent by weight iron oxide, and about 0.12 per cent by weight K 0 and Na O such as ALUNDUM marketed by the Norton Company of Worcester, Mass, 01606.

Reference is made to the many Norton Product Information publications such as l-CTM-P3, S-P-A-BDI, S-P-A-BD2, S-P-A-BD3, S-P-A-BD4, S-P-A-BDS, S-P- A-BD6, S-P-A-CTl.l, S-P-A-CTLZ, S-P-A-C'Tl.3, S- P-A-CT2.1, S-P-A-CT2.2, S-P-A-CT3, and S-P-A- GRl.

In another embodiment, there is used a silicon carbide such as CRYSTAR, CRYSTON, and CRYSTO- LON products containing 60 to 99 per cent by weight silicon carbide and marketed by the Norton Company. Reference is made to Norton Product Information publications S-P-C-BDI, S-P-C-BDZ, S-P-C-BDB, S-P-C- CTl, S-P-C-GRl, S-AP-G2.7, and S-P-SC-BDI. Also reference is made to Norton publications S-AP-G2.l and H-l.l-l I.

In another embodiment, there is used a boron nitride such as marketed by the Refractories and Electronics Division of the Carborundum Company, especially Grades A, M, and HP.

In another embodiment, there is used a fused magnesium oxide such as MAGNORITE marketed by the Norton Company, publication I-TC-Pl, consisting essentially of about 99 per cent by weight magnesium oxide.

In another embodiment, there is used a fused zirconia such as ZIRNORITE marketed by the Norton Company, containing about to about per cent by weight zirconia. See Norton publications S-P-Z-BDI, S-P-Z-CTI, and S-P-Z-GRI.

Other contemplated materials include titanium oxide, hafnium oxide, and Group II oxides, boron carbide, and graphite.

Ideally, a base plate material is sleected which will retain its relative surface flatness and contour within about 0.5 to about 2 mils over a temperature range of about 1,000 F. to about 2,000 F.

The drawing illustrates practice of the invention as applied to one of the glass plates forming a part of a gas discharge display/memory device. As illustrated, glass plate 10 with electrode array 11 thereon has a thin coating of a glass dielectric coating 12 uniformly applied as by a spray of silk screening process to cover at least the portion of conductors in array 11 to be included within the active display area of the device. Glass dielectric coating 12 has expansion characteristics to match those of glass support plate 10. Support plate 10 rests on a flat base plate 13 which as described above, is constituted by a material which maintains its relative surface flatness and lubricity at the elevated firing temperatures so as to promote the relative surface flatness and smoothness of the substrate and dielectric layer during the firing thereof.

In the practice of this invention, it has been discovered that the use of the base plate as described hereinbefore, not only maintains the relative surface flatness of the glass substrate and the electrodes and/or dielectric applied thereto, but will also tend to provide a flat surface; that is, when the glass substrate is heated above its annealing temperature while supported by its base plate, there is a tendency for the substrate surface to become more flat. As noted hereinbefore, this invention especially results in the preparation of a memory panel having more uniform spacing and, therefore, more uniform operating characteristics.

We claim:

11. In a process for preparing an electronic device wherein conductive electrode members and a dielectric layer are applied to a flat surface on a glass substrate, the surface on the opposite side thereof also having a flat surface, the improvement which comprises firing the electrode members and the dielectric layer onto the flat glass substrate surface at elevated temperatures within a range of about 1,000 F to about 2,000 F while the opposite flat surface of the glass substrate is supported by a flat surface of a base plate, said base plate comprising a material which maintains its surface flatness and contour within a range of about 0.5 to about 2 mils over the temperature range of about 1,000 F to about 2,000 F, said material also having a surface lubricity such that the opposite surface of the glass substrate does not stick or adhere to the surface of the base plate but does not readily slide off the surface of the base plate, wherebythe relative smoothness of the flat surface of the glass substrate and the dielectric coating fired thereon are enhanced.

2. The process of claim I wherein the base plate material is selected from refractory, ceramic, glass, and glass-ceramic.

3. The process of claim 2 wherein the material is selected from aluminum silicate, magnesium silicate, aluminum-magnesium silicate, fused silicon oxide, aluminum oxide, silicon carbide, boron nitride, zirconium oxide, titanium oxide, hafrium oxide, boron carbide, graphite, and Group ll oxides.

4. The process of claim 1 wherein the material is magnesium oxide.

5. In a process for preparing a gaseous discharge panel comprising two spaced glass substrates having electrode elements and a dielectric layer fired thereon at high elevated temperatures above the annealing temperature of the glass substrate, the distance between the opposing dielectric members being substantially equal and uniform, the improvement which comprises firing the electrode elements and dielectric layer onto a flat surface on a glass substrate, the surface on the opposite side thereof also having a flat surface and being supported by a flat surface of a base plate of material which at the elevated temperatures maintains its relative surface flatness and contour within a range of about 0.5 to about 2 mils over a temperature range of about 1,000 F to about 2,000 F, the base plate material having a surface lubricity such that the opposite surface of the glass substrate does not stick or adhere to the surface of the base plate but does not readily slide off the surface of the base plate at the elevated firing temperatures so as to promote the relative surface flatness and smoothness of the flat surface of the glass substrate and dielectric layer fired thereon, such that the overall uniformity of the panel spacing and the panel operating characteristics are enhanced.

6. The process of claim 5 wherein the base plate material is a silicon-containing refractory.

7. The process of claim 6 wherein the refractory is a fired ceramic lava silicate.

8. The process of claim 7 wherein the fired ceramic lava silicate is selected from aluminum silicate, magnesium silicate, and aluminum-magnesium silicate.

9. In a process for preparing an electronic device containing electrode members applied to the surface of a glass substrate, said surface having a predetermined contour and said glass substrate having a surface on the opposite side thereof with the same contour, the improvement which comprises applying the electrode members to the one surface of the glass substrate at a high elevated temperature of about 1,000 F to about 2,000 F, while the opposite surface of the glass substrate is supported by the surface of a base plate which maintains its surface contour within about 0.5 to about 2 mils over the high elevated temperature range of about 1,000 F to about 2,000 F, said base plate having a surface lubricity such that the glass substrate does not stick or adhere thereto, but does not readily slide off of the base plate surface, whereby the relative smoothness of the glass substrate surface is enhanced.

10. The process of claim 1 wherein the base plate surface is unpolished. 

2. The process of claim 1 wherein the base plate material is selected from refractory, ceramic, glass, and glass-ceramic.
 3. The process of claim 2 wherein the material is selected from aluminum silicate, magnesium silicate, aluminum-magnesium silicate, fused silicon oxide, aluminum oxide, silicon carbide, boron nitride, zirconium oxide, titanium oxide, hafrium oxide, boron carbide, graphite, and Group II oxides.
 4. The process of claim 1 wherein the material is magnesium oxide.
 5. In a process for preparing a gaseous discharge panel comprising two spaced glass substrates having electrode elements and a dielectric layer fired thereon at high elevated temperatures above the annealing temperature of the glass substrate, the distance between the opposing dielectric members being substantially equal and uniform, the improvement which comprises firing the electrode elements and dielectric layer onto a flat surface on a glass substrate, the surface on the opposite side thereof also having a flat surface and being supported by a flat surface of a base plate of material which at the elevated temperatures maintains its relative surface flatness and contour within a range of about 0.5 to about 2 mils over a temperature range of about 1,000* F to about 2,000* F, the base plate material having a surface lubricity such that the opposite surface of the glass substrate does not stick or adhere to the surface of the base plate but does not readily slide off the surface of the base plate at the elevated firing temperatures so as to promote the relative surface flatness and smoothness of the flat surface of the glass substrate and dielectric layer fired therEon, such that the overall uniformity of the panel spacing and the panel operating characteristics are enhanced.
 6. The process of claim 5 wherein the base plate material is a silicon-containing refractory.
 7. The process of claim 6 wherein the refractory is a fired ceramic lava silicate.
 8. The process of claim 7 wherein the fired ceramic lava silicate is selected from aluminum silicate, magnesium silicate, and aluminum-magnesium silicate.
 9. In a process for preparing an electronic device containing electrode members applied to the surface of a glass substrate, said surface having a predetermined contour and said glass substrate having a surface on the opposite side thereof with the same contour, the improvement which comprises applying the electrode members to the one surface of the glass substrate at a high elevated temperature of about 1,000* F to about 2,000* F, while the opposite surface of the glass substrate is supported by the surface of a base plate which maintains its surface contour within about 0.5 to about 2 mils over the high elevated temperature range of about 1,000* F to about 2,000* F, said base plate having a surface lubricity such that the glass substrate does not stick or adhere thereto, but does not readily slide off of the base plate surface, whereby the relative smoothness of the glass substrate surface is enhanced.
 10. The process of claim 1 wherein the base plate surface is unpolished. 